Conventionally, light sources are known in which semiconductor light emitting elements such as LEDs (Light Emitting Diodes) are employed as lighting devices for vehicles. In this sort of vehicle-purpose lighting devices, a control apparatus for controlling lighting operations of the LEDs is mounted.
Lighting control apparatus equipped with switching regulators are known. The switching regulators are capable of controlling output voltages with respect to LEDs based upon currents of the LEDs. Even when multiple LEDs are connected as a load either in series manner or in parallel, the switching regulators can control output voltages so that specified currents may flow through the respective LEDs.
However, if outputs of the switching regulators are short-circuited, or grounded, then the loads of the switching regulators are increased. As a result, there is the possibility that the switching regulators will malfunction in combination with excessively heavy power loads. Also, when the outputs of the switching regulators are brought into open statuses due to disconnections of LEDs, for instance, in a flyback-type switching regulator, the output voltage can be increased excessively.
Under such a circumstance, it has been proposed to lower an output voltage of the switching regulator when an abnormal condition is detected on the output side of a switching regulator is detected (see, e.g., Japanese patent document JP-A-2004-134147, in particular FIG. 1, FIG. 6, and FIG. 7, pages 3 to 8).).
In the foregoing conventional technique, multiple LED blocks are connected in parallel to the output side of the switching regulator. A series regulator, which contains a switch element, a shunt resistor, and a comparator, is connected in series to each of the LED blocks. The output voltage of the switching regulator is controlled so that the current of each of the LED blocks constitutes a defined current. When an abnormal condition occurs, the output voltage of the switching regulator is lowered. As a result, even if some of the LEDs malfunction, the sound LEDs can be protected. However, the foregoing conventional technique does not address detection of an abnormal condition with respect to each of the LED blocks.